A functional comparison between bat assemblages of Andean arid enclaves

Resumen

Climatic characteristics and low environmental complexity of tropical xerophitic ecosystems determine the functional structure of bat assemblages, which may be mainly affected by lack of food and shelter in relation to wet environments. Several xerophitic enclaves with similar physiognomy occur along the Andes of northern South America. These similarities suggest that differences in bat composition are due to biogeographic effect, while similarities in functional structure are due to equivalent selective pressures. Data on bat assemblages of these environments is scarce and fragmented. The goal of this work was to gather complete lists of bat species for five inter-Andean xerophitic enclaves and compare both composition and functional structure between them. The five arid Andean enclaves are located along the Cordillera Oriental (Colombia) and Cordillera de Mérida (Venezuela). For comparisons, we also used data from literature for seven additional lists from other continental and insular arid locations of northern Venezuela and the Caribbean. In each location, we caught bats by mist netting monthly or bimonthly during a year to get the composition of each bat assemblage. We used rarefaction curves to determine when species accumulation reached a plateau and the Chao2 and Jackknife2 index to estimate the species richness. For taxonomic and functional comparisons we used clustering analysis of the different arid environments considered and a wet lowland rainforest as an external group, using the distance of dissimilarity of Bray-Curtis and group average linkage method. Although results of both taxonomic and functional analysis were similar showing two main groups of assemblages which can be distinguished by their differences in the importance of nectarivores, frugivores and hematophages guilds, however, functional analysis was much more reliable than taxonomic. Additionally, we detected that when a xerophitic site was in contact with wet environments, “alien species” were included in the assemblage, affecting the taxonomic and functional structures. Thus, when these alien species are not taken into account, the essential assemblage of a tropical xeric environment is composed by insectivorous and nectarivorous bat species.